1. Field of the Invention
This application is based on Japanese Patent Application No. 11-111498 (1999) filed Apr. 19, 1999, the content of which is incorporated hereinto by reference.
The present invention relates to a test pattern printing method, an information processing apparatus and a printing apparatus, and more specifically to a test pattern printing method to print a test pattern which is checked for detecting a color deviation, the deviation being caused by variations in an output characteristic among print heads, and an information processing apparatus and a printing apparatus to perform printing of the test pattern.
2. Description of the Related Art
As devices for automated office work have come into wide use, an opportunity of producing color images in an office has increased. Output devices for outputting color images is known as a printing apparatus of various methods, such as an ink jet method, an electro-photographic method and a heat transfer method. These printing apparatuses have become able to output picture-like color images of relatively high quality in recent years.
Such printing apparatus generally prints color images using three colorants of chromatic colors, cyan(C), magenta(M) and yellow(Y), or four colorants with an additional achromatic color, black(K). The printed color image, however, may have a color deviation or color misrepresentation (e.g., produced color in the printed image differs from a desired one) due to an imbalance of output characteristics (reflection density or lightness, saturation, hue, etc.) among print heads for respective colors. In the ink jet system, for example, the print heads may have, among themselves, differences in an amount of heat produced by heaters (film thickness of the heater) for ejecting ink and differences in a size and shape of ink ejection orifices, causing differences in an amount of ejected ink. This in turn may result in the output characteristic imbalance among the print heads for individual color, as described above. Not only do the print heads inherently having such differences, but it is also known that these differences are produced with elapse of time.
To cope with this problem, a personal computer functioning as a host computer for the printing apparatus, or the printing apparatus itself, may perform correction processing which involves detecting the color deviation due to the differences among respective print heads and, based on the result of detection, correcting the output characteristics of the print heads to have predetermined characteristics. The correction processing is generally known to be carried out in two ways, which are distinguished depending primarily on whether the detection of the color deviation is done by using an input device such as scanner or by a human visual check. An outline of these two correction methods, as distinguished by the way of detecting the color deviation, will be briefly explained below.
The method using an input device such as a scanner, for example, first prints a patch pattern by using the print heads of C, M, Y and K coloring materials that are subjects of the correction, as disclosed in the official gazette of Japanese Patent No. 2661917. Then, the patch pattern is read by means of the scanner to detect a difference between a read value (representing an output characteristic of the head) and an expected value calculated from the print data for the patch pattern. Based on the detected difference, the color deviation is corrected. The patch pattern used in this method may be a solid pattern of each of C, M, Y, K colors or a patch pattern of each color having patches showing a gradation in density. The gradation patch pattern can also be used to detect an output characteristic with respect to a halftone, thus improving precision of detecting the color deviation. A method is also known as that combines the C, M, Y and K to form second- or third-color patch patterns and thereby improves the detection and correction accuracy.
On the other hand, the method using the visual check, unlike the method using the input device, can not easily detect an absolute value with respect to the output characteristic for each color head. Hence, a detection method that uses a third-color patch pattern printed by mixing three colorants C, M, Y is mostly used. More specifically, a plurality of patches of almost gray color is printed. The plurality of patches includes a patch as a central patch of the plurality of patches, which is expected to be printed at a predetermined ratio of three colorants (represented by print data of three colorants) so as to be a patch of an achromatic color when the patch is printed by using print heads with an average ink ejection amount or without any deviation of ink ejection amount, and other patches which are printed with their three-color ratios successively changed slightly. From the plurality of patches a user visually chooses one patch closest to the achromatic color so as to detect the patch of the most appropriate output characteristic balance among the C, M, Y color print heads. Then, the correction data corresponding to the detected patch is used to correct the output characteristic of each print head. This method of detecting the color deviation takes advantage of the fact that a slight imbalance in the output characteristic among the C, M, Y color print heads causes the color having a relatively large output characteristic change to appear in the patch, resulting in the patch deviating from the achromatic color.
While the color deviation and the method of its detection have been described for the case of the print heads of ink jet system, differences in the output characteristics of the color print heads may also occur with the printing apparatus of electrophotographic system and heat transfer system due to causes peculiar to the operation principles of the respective printing systems. In these printing systems, also, the color deviation detection and correction are performed in a similar manner.
The conventional color deviation detection method described above, however, has the following drawbacks.
First, in a usual environment in which the printing apparatus is used, the method using an input device such as scanner requires a condition that the user owns the input device. Not all users have the input device available and thus the method using the scanner or other input devices is not realistic. If some input device is made available, the correction process on a basis of the color deviation detection using such wide variation of input devices is often very difficult to be carried out.
The method based on visual check, on the other hand, does not require any special input device and thus can be employed by any user to detect the color deviation. It is however not so easy to select a patch closest to achromatic color from a plurality of patches with their C, M, Y color ratios progressively changed slightly.
For example, JIS (JIS E3305, JIS Z8721, JIS L0600, etc.) and various other organizations provide specifications concerning a color difference (AE). In these specifications, a range of the color difference of 3.2-6.5 is defined as a xe2x80x9crange that can be handled as the same color in terms of impression.xe2x80x9d This suggests that visually picking up a patch closest to achromatic color from patches in this range of color difference is difficult. It is also stated that the color difference in such a range may xe2x80x9ccause a customer to complain about difference in color when selecting paint color,xe2x80x9d suggesting that even in this range of color difference, if a wrong patch is selected, an image printed after being corrected by a correction value corresponding to the selected patch may fail to provide a desired color.
For this reason, an effort is being made to improve the accuracy of the visual check-based color deviation detection method.
FIG. 1 is a view schematically showing an example of test pattern that enables an improvement of precision for detecting the color deviation. In FIG. 1, each frame represents a patch printed with a mixture of C, M and Y colors and with K. Four numbers in each of two areas in each patch represent multi-valued gradation data for printing the associated area and correspond, from top to bottom, to C, M, Y and K. Thus, the patch shown in FIG. 1 consists of two upper and lower areas. Then, a test pattern is made up of an array of such patches with their gradation value of M increasing vertically downward in five steps and that of C increasing horizontally toward right in five steps.
As apparent from FIG. 1, a test area defined by the upper area in each patch is an area printed with a mixture of C, M, Y colorants of chromatic colors (the mixed color is hereinafter referred to as xe2x80x9cPCBkxe2x80x9d that is xe2x80x9cprocess blackxe2x80x9d). A reference area defined by the lower area is an area printed with only K, a colorant of achromatic color. In the upper area printed with PCBk the gradation value of Y is fixed at a 128 level. Further, as described above, value of C in the pattern increases toward the right and value of M increases downwardly.
With the test pattern constructed in this way, the precision of visual detection can be improved. More specifically, this pattern takes advantage of a visual characteristic that when objects are close together, a small color difference can be perceived. More concretely, this pattern is based on a fact that even if the color difference is as small as 0.8-1.6, comparison between adjacent objects allows a human eye to perceive the color difference. The pattern of this method allows the user, rather than to search, without any criterion, through a plurality of patches printed with only PCBk to find a patch closest to achromatic color, to make one-tone comparison between an area printed with an achromatic color K and an area printed with PCBk which areas are adjacent to each other and thereby select a patch with a PCBk area having the least color difference from the area of achromatic color K. Thus, the precision of visual detection can be improved. This method is hereinafter called an xe2x80x9cadjacency comparison methodxe2x80x9d.
As described above, the precision of visual detection of color difference (color deviation) can generally be improved by using the adjacency comparison method. However, the conventional test pattern shown in FIG. 1 has some points to be improved in performing appropriate color deviation detection.
More specifically, the adjacency comparison method, as described above, has relatively high detection accuracy and therefore the detection accuracy may not match a variation width of the output characteristic of the printing apparatus for each colorant. For example, the output characteristic may vary relatively widely depending on the printing apparatus and, in such a case, the color difference between the patches are set large to make the correction width correspondingly large. In this case, because the detection accuracy of the adjacency comparison method is high, the color of the test area may look different at some degree from the achromatic color of the reference area in any of the patch, making it impossible to identify one patch that corresponds to the color deviation.
Also, when the perceptive characteristics for the two areas during the adjacency comparison are not equal, a correct comparison cannot be made.
The adjacency comparison method is intended to identify a test area that exhibits the color most close to an achromatic color. That is, it is desired that the color difference of the test area with respect to the reference area is perceived as a difference in a saturation, one of a variety kinds of color representing elements. However, it may not be possible with the conventional test pattern shown in FIG. 1 because the human perceptive characteristic of recognizing the patch color may not be able to strongly perceive the saturation difference, depending on the patch being checked.
The object of the present invention is to provide a test pattern printing method, an information processing apparatus and a printing apparatus capable of printing a test pattern that allows the visual color deviation detection to be performed appropriately and highly accurately during the processing for correcting a color deviation caused by output characteristic variations of the printing apparatus among the colorants.
In the first aspect of the present invention, there is provided a test pattern printing method of printing a test pattern used in correction processing, the correction processing making an output characteristic for each of a plurality of colorants a predetermined one to correct a color deviation, the method comprising the step of:
printing a plurality of patches each of which has a test area and a reference area placed adjacent to each other, the test area being printed with a mixture of the plurality of colorants and serving as an indicator for indicating a degree of the color deviation and the reference area serving as a reference to be compared with the test area for the color deviation, the plurality of patches being printed at different mixing ratios of the plurality of colorants, respectively;
wherein the test area and the reference area are arranged in each of the plurality of patches so that the test area and the reference area are repeated alternately.
In the second aspect of the present invention, there is provided an information processing apparatus for performing a process of printing a test pattern used in correction processing, the correction processing making an output characteristic for each of a plurality of colorants a predetermined one to correct a color deviation in printing by a printing apparatus, the apparatus including:
a unit for causing the printing apparatus to print a plurality of patches each of which has a test area and a reference area placed adjacent to each other, the test area being printed with a mixture of the plurality of colorants and serving as an indicator for indicating a degree of the color deviation and the reference area serving as a reference to be compared with the test area for the color deviation, the plurality of patches being printed at different mixing ratios of the plurality of colorants, respectively;
wherein the test area and the reference area are arranged in each of the plurality of patches so that the test area and the reference area are repeated alternately.
In the third aspect of the present invention, there is provided a printing apparatus capable of printing a test pattern used in correction processing, the correction processing making an output characteristic for each of a plurality of colorants a predetermined one to correct a color deviation, the apparatus including:
a unit for printing a plurality of patches each of which has a test area and a reference area placed adjacent to each other, the test area being printed with a mixture of the plurality of colorants and serving as an indicator for indicating a degree of the color deviation and the reference area serving as a reference to be compared with the test area for the color deviation, the plurality of patches being printed at different mixing ratios of the plurality of colorants, respectively;
wherein the test area and the reference area are arranged in each of the plurality of patches so that the test area and the reference area are repeated alternately.
According to the above construction, the patches each have a test area and a reference area arranged adjacent to each other and these two areas are repeated alternately. Hence, a degree to which the colors of the two areas when compared tend to be perceived as different is alleviated according to a number of repetitions of the two areas. Therefore, for example, when a correction amount at which an output characteristic variation is corrected based on the patch selection is set at not so large a value, the number of repetitions of the two areas of each of patches can be determined according to the correction amount. Among these patches, when selecting a patch that exhibits the most color uniformity with not so large perceivable color difference between the two areas, the selected patch is one corresponding to the color deviation equivalent to the correction amount.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.